ELM 300/300-1 Features
1 Single trip point alarm for ground check
Voltage build-up detection
Optional end-of-line resistor for crush fault detection
ac 120V input power (ELM 300), dc 24V input power (ELM 300-1)
The ELM 300/300-1 ground check relay has been designed to ensure continuous ground integrity checking for fixed or portable equipment.
Ground Checking Operation
The ELM 300/300-1 has several protective methods to ensure proper grounding of fixed or portable equipment. If the unit senses any one of the following conditions, it activates the alarm relay (K1) with a response time of < 30
• Pilot Wire Ground Integrity Check
The ELM 300/300-1 monitors the resistance of the return path to ground via a ground connection from terminal 9 and a standard loop pilot wire going to the equipment from terminal 7. The unit continuously sends a measuring signal around the ground loop circuit. This circuit comprises the main equipment grounding conductor, a section of the equipment casing and a pilot conductor return path. When the ELM 300/300-1 detects a loop resistance in excess of 1, it will activate the output alarm relay (K1).
Earth Voltage Build-up
The ELM 300/300-1 can also detect large ground fault currents that may cause unsafe voltage build-up on the ground path. If the unit senses a voltage (6 V ac - 30 V ac) on the ground path, it will immediately react to this condition.
Optional End-of-Line Resistor (EOL)
The ELM 300/300-1 ground checking operation has an additional protection feature. The unit can detect crush or parallel faults. This situation occurs when the cable ground wire becomes unintentionally connected to the equipment pilot wire. To sense this fault, a grounding resistor is connected to the pilot wire from terminal
8 instead of terminal 7. In this configuration, the ELM 300/300-1 will alarm if the ground wire ever comes into contact with the equipment pilot wire. This grounding resistor must have a value of 49.9
with a high tolerance of +/- 0.1% to ensure proper function of the ELM 300/300-1. We can supply this resistor on request. Please note: this end-of-line (EOL) will not affect the operation of the earth voltage build-up function.